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PaleontologyFrom Wikipedia, the free encyclopedia

"Palaeontology" redirects here. For the scientific journal, see Palaeontology (journal).

Paleontology or palaeontology (/ˌpeɪlɪɒnˈtɒlədʒi/, /ˌpeɪlɪənˈtɒlədʒi/ or /ˌpælɪɒnˈtɒlədʒi/, /ˌpælɪənˈtɒlədʒi/)is the scientific study of life existent prior to, and sometimes including, the start of the Holocene Epochroughly 11,700 years before present. It includes the study of fossils to determine organisms' evolution andinteractions with each other and their environments (their paleoecology). Paleontological observations havebeen documented as far back as the 5th century BC. The science became established in the 18th century as aresult of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Theterm itself originates from Greek παλαιός, palaios, i.e. "old, ancient", ὄν, on (gen. ontos), i.e. "being,creature" and λόγος, logos, i.e. "speech, thought, study".[1]

Paleontology lies on the border between biology and geology, but differs from archaeology in that itexcludes the study of morphologically modern humans. It now uses techniques drawn from a wide range ofsciences, including biochemistry, mathematics and engineering. Use of all these techniques has enabledpaleontologists to discover much of the evolutionary history of life, almost all the way back to when Earthbecame capable of supporting life, about 3,800 million years ago. As knowledge has increased,paleontology has developed specialised sub-divisions, some of which focus on different types of fossilorganisms while others study ecology and environmental history, such as ancient climates.

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemicalevidence has helped to decipher the evolution of life before there were organisms large enough to leavebody fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layersallow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more oftenpaleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy.Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that iscommonly used for classifying living organisms, and paleontologists more often use cladistics to draw upevolutionary "family trees". The final quarter of the 20th century saw the development of molecularphylogenetics, which investigates how closely organisms are related by measuring how similar the DNA isin their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged,but there is controversy about the reliability of the molecular clock on which such estimates depend.

Contents1 Overview

1.1 A historical science1.2 Related sciences1.3 Subdivisions

2 Sources of evidence2.1 Body fossils2.2 Trace fossils2.3 Geochemical observations

3 Classifying ancient organisms4 Estimating the dates of organisms5 Overview of the history of life

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A palaeontologist at work at JohnDay Fossil Beds National Monument

The preparation of the fossilisedbones of Europasaurus holgeri

5 Overview of the history of life5.1 Mass extinctions

6 History of paleontology7 See also8 Notes9 References10 External links

Overview

The simplest definition is "the study of ancient life".[2] Paleontologyseeks information about several aspects of past organisms: "theiridentity and origin, their environment and evolution, and what theycan tell us about the Earth's organic and inorganic past".[3]

A historical science

Paleontology is one of the historical sciences, along witharchaeology, geology, astronomy, cosmology, philology and historyitself.[4] This means that it aims to describe phenomena of the pastand reconstruct their causes.[5] Hence it has three main elements:description of the phenomena; developing a general theory about thecauses of various types of change; and applying those theories tospecific facts.[4]

When trying to explain past phenomena, paleontologists and otherhistorical scientists often construct a set of hypotheses about thecauses and then look for a smoking gun, a piece of evidence thatindicates that one hypothesis is a better explanation than others.Sometimes the smoking gun is discovered by a fortunate accidentduring other research. For example, the discovery by Luis Alvarezand Walter Alvarez of an iridium-rich layer at theCretaceous–Tertiary boundary made asteroid impact and volcanismthe most favored explanations for the Cretaceous–Paleogeneextinction event.[5]

The other main type of science is experimental science, which is often said to work by conductingexperiments to disprove hypotheses about the workings and causes of natural phenomena – note that thisapproach cannot confirm a hypothesis is correct, since some later experiment may disprove it. However,when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation,experimental scientists often use the same approach as historical scientists: construct a set of hypothesesabout the causes and then look for a "smoking gun".[5]

Related sciences

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Analyses using engineeringtechniques show that Tyrannosaurushad a devastating bite, but raisedoubts about how fast it could move.

Paleontology lies on the boundary between biology and geology since paleontology focuses on the record ofpast life but its main source of evidence is fossils, which are found in rocks.[6] For historical reasonspaleontology is part of the geology departments of many universities, because in the 19th century and early20th century geology departments found paleontological evidence important for estimating the ages of rockswhile biology departments showed little interest.[7]

Paleontology also has some overlap with archaeology, which primarily works with objects made by humansand with human remains, while paleontologists are interested in the characteristics and evolution of humansas organisms. When dealing with evidence about humans, archaeologists and paleontologists may worktogether – for example paleontologists might identify animal or plant fossils around an archaeological site,to discover what the people who lived there ate; or they might analyze the climate at the time when the sitewas inhabited by humans.[8]

In addition paleontology often uses techniques derived from othersciences, including biology, osteology, ecology, chemistry, physicsand mathematics.[2] For example, geochemical signatures from rocksmay help to discover when life first arose on Earth,[9] and analysesof carbon isotope ratios may help to identify climate changes andeven to explain major transitions such as the Permian–Triassicextinction event.[10] A relatively recent discipline, molecularphylogenetics, often helps by using comparisons of different modernorganisms' DNA and RNA to re-construct evolutionary "familytrees"; it has also been used to estimate the dates of importantevolutionary developments, although this approach is controversialbecause of doubts about the reliability of the "molecular clock".[11]Techniques developed in engineering have been used to analyse howancient organisms might have worked, for example how fast Tyrannosaurus could move and how powerfulits bite was.[12][13] It is relatively commonplace to study fossils using X-ray microtomography[14] Acombination of paleontology, biology, and archaeology, paleoneurology is the study of endocranial casts (orendocasts) of species related to humans to learn about the evolution of human brains.[15]

Paleontology even contributes to astrobiology, the investigation of possible life on other planets, bydeveloping models of how life may have arisen and by providing techniques for detecting evidence of life.[16]

Subdivisions

As knowledge has increased, paleontology has developed specialised subdivisions.[17] Vertebratepaleontology concentrates on fossils of vertebrates, from the earliest fish to the immediate ancestors ofmodern mammals. Invertebrate paleontology deals with fossils of invertebrates such as molluscs,arthropods, annelid worms and echinoderms. Paleobotany focuses on the study of fossil plants, buttraditionally includes the study of fossil algae and fungi. Palynology, the study of pollen and spores

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This Marrella specimen illustrateshow clear and detailed the fossilsfrom the Burgess Shale lagerstätteare.

produced by land plants and protists, straddles the border between paleontology and botany, as it deals withboth living and fossil organisms. Micropaleontology deals with all microscopic fossil organisms, regardlessof the group to which they belong.[18]

Instead of focusing on individual organisms, paleoecology examines the interactions between differentorganisms, such as their places in food chains, and the two-way interaction between organisms and theirenvironment.[19]  One example is the development of oxygenic photosynthesis by bacteria, which hugelyincreased the productivity and diversity of ecosystems.[20] This also caused the oxygenation of theatmosphere. Together, these were a prerequisite for the evolution of the most complex eukaryotic cells, fromwhich all multicellular organisms are built.[21]

Paleoclimatology, although sometimes treated as part of paleoecology,[18] focuses more on the history ofEarth's climate and the mechanisms that have changed it[22] – which have sometimes included evolutionarydevelopments, for example the rapid expansion of land plants in the Devonian period removed more carbondioxide from the atmosphere, reducing the greenhouse effect and thus helping to cause an ice age in theCarboniferous period.[23]

Biostratigraphy, the use of fossils to work out the chronological order in which rocks were formed, is usefulto both paleontologists and geologists.[24] Biogeography studies the spatial distribution of organisms, and isalso linked to geology, which explains how Earth's geography has changed over time.[25]

Sources of evidence

Body fossils

Main article: Fossils

Fossils of organisms' bodies are usually the most informative type ofevidence. The most common types are wood, bones, and shells.[26]Fossilisation is a rare event, and most fossils are destroyed byerosion or metamorphism before they can be observed. Hence thefossil record is very incomplete, increasingly so further back in time.Despite this, it is often adequate to illustrate the broader patterns oflife's history.[27] There are also biases in the fossil record: differentenvironments are more favorable to the preservation of differenttypes of organism or parts of organisms.[28] Further, only the parts oforganisms that were already mineralised are usually preserved, suchas the shells of molluscs. Since most animal species are soft-bodied,they decay before they can become fossilised. As a result, althoughthere are 30-plus phyla of living animals, two-thirds have never beenfound as fossils.[29]

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Cambrian trace fossils includingRusophycus, made by a trilobite

Amphibians

Synapsids Extinct Synapsids

Occasionally, unusual environments may preserve soft tissues. These lagerstätten allow paleontologists toexamine the internal anatomy of animals that in other sediments are represented only by shells, spines,claws, etc. – if they are preserved at all. However, even lagerstätten present an incomplete picture of life atthe time. The majority of organisms living at the time are probably not represented because lagerstätten arerestricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved veryquickly by events such as mudslides; and the exceptional events that cause quick burial make it difficult tostudy the normal environments of the animals.[30] The sparseness of the fossil record means that organismsare expected to exist long before and after they are found in the fossil record – this is known as the Signor-Lipps effect.[31]

Trace fossils

Main article: Trace fossil

Trace fossils consist mainly of tracks and burrows, but also includecoprolites (fossil feces) and marks left by feeding.[26][32] Tracefossils are particularly significant because they represent a datasource that is not limited to animals with easily fossilised hard parts,and they reflect organisms' behaviours. Also many traces date fromsignificantly earlier than the body fossils of animals that are thoughtto have been capable of making them.[33] Whilst exact assignment oftrace fossils to their makers is generally impossible, traces may forexample provide the earliest physical evidence of the appearance ofmoderately complex animals (comparable to earthworms).[32]

Geochemical observations

Main article: Geochemistry

Geochemical observations may help to deduce the global level of biological activity, or the affinity ofcertain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth,[9] andmay provide evidence of the presence of eukaryotic cells, the type from which all multicellular organismsare built.[34] Analyses of carbon isotope ratios may help to explain major transitions such as the Permian–Triassic extinction event.[10]

Classifying ancient organismsMain articles: Biological classification, Cladistics, Phylogenetic nomenclature and Evolutionarytaxonomy

Naming groups of organisms in a waythat is clear and widely agreed isimportant, as some disputes inpaleontology have been based just onmisunderstandings over names.[36]

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TetrapodsAmniotes

    Mammals

Reptiles

Extinct reptiles

Lizards and snakes

Archosaurs ? 

ExtinctArchosaurs

Crocodilians

Dinosaurs ? 

ExtinctDinosaurs

 ?  Birds

Simple example cladogram    Warm-bloodedness evolved somewhere in thesynapsid–mammal transition. ?  Warm-bloodedness must also have evolved at one ofthese points – an example of convergent evolution.[35]

Levels in theLinneantaxonomy

Linnean taxonomy is commonly usedfor classifying living organisms, butruns into difficulties when dealing withnewly discovered organisms that aresignificantly different from known ones.

For example: it ishard to decide atwhat level to placea new higher-levelgrouping, e.g.genus or family ororder; this isimportant since theLinnean rules fornaming groups aretied to their levels,and hence if agroup is moved to adifferent level itmust be renamed.[37]

Paleontologistsgenerally useapproaches based

on cladistics, a technique for working out the evolutionary "family tree" of a set of organisms.[36] It worksby the logic that, if groups B and C have more similarities to each other than either has to group A, then Band C are more closely related to each other than either is to A. Characters that are compared may beanatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or proteins.The result of a successful analysis is a hierarchy of clades – groups that share a common ancestor. Ideallythe "family tree" has only two branches leading from each node ("junction"), but sometimes there is toolittle information to achieve this and paleontologists have to make do with junctions that have severalbranches. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes,evolved more than once, convergently – this must be taken into account in analyses.[35]

Evolutionary developmental biology, commonly abbreviated to "Evo Devo", also helps paleontologists toproduce "family trees", and understand fossils.[38] For example, the embryological development of somemodern brachiopods suggests that brachiopods may be descendants of the halkieriids, which became extinctin the Cambrian period.[39]

Estimating the dates of organismsMain article: Geochronology

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Common index fossils used to date rocks in North-East USA

Paleontology seeks to map out how living things have changed through time. A substantial hurdle to thisaim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack theradioactive elements needed for radiometric dating.This technique is our only means of giving rocksgreater than about 50 million years old an absoluteage, and can be accurate to within 0.5% or better.[40]Although radiometric dating requires very carefullaboratory work, its basic principle is simple: therates at which various radioactive elements decay areknown, and so the ratio of the radioactive element tothe element into which it decays shows how long agothe radioactive element was incorporated into therock. Radioactive elements are common only in rockswith a volcanic origin, and so the only fossil-bearingrocks that can be dated radiometrically are a fewvolcanic ash layers.[40]

Consequently, paleontologists must usually rely onstratigraphy to date fossils. Stratigraphy is the scienceof deciphering the "layer-cake" that is thesedimentary record, and has been compared to ajigsaw puzzle.[41] Rocks normally form relatively horizontal layers, with each layer younger than the oneunderneath it. If a fossil is found between two layers whose ages are known, the fossil's age must liebetween the two known ages.[42] Because rock sequences are not continuous, but may be broken up byfaults or periods of erosion, it is very difficult to match up rock beds that are not directly next to oneanother. However, fossils of species that survived for a relatively short time can be used to link up isolatedrocks: this technique is called biostratigraphy. For instance, the conodont Eoplacognathus pseudoplanus hasa short range in the Middle Ordovician period.[43] If rocks of unknown age are found to have traces of E.pseudoplanus, they must have a mid-Ordovician age. Such index fossils must be distinctive, be globallydistributed and have a short time range to be useful. However, misleading results are produced if the indexfossils turn out to have longer fossil ranges than first thought.[44] Stratigraphy and biostratigraphy can ingeneral provide only relative dating (A was before B), which is often sufficient for studying evolution.However, this is difficult for some time periods, because of the problems involved in matching up rocks ofthe same age across different continents.[45]

Family-tree relationships may also help to narrow down the date when lineages first appeared. For instance,if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of Band C, then A must have evolved more than X million years ago.

It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long agotheir last common ancestor must have lived  – by assuming that DNA mutations accumulate at a constantrate. These "molecular clocks", however, are fallible, and provide only a very approximate timing: forexample, they are not sufficiently precise and reliable for estimating when the groups that feature in theCambrian explosion first evolved,[46] and estimates produced by different techniques may vary by a factorof two.[11]

Cenozoic

Mesozoic

Paleozoic

Proterozoic

Quater-naryTertiary

Creta-ceousJurassic

Triassic

PermianMissis-sippianPennsyl-vanianDevo-nianSilurianOrdo-vicianCamb-rian

Pecten gibbus

CalyptraphorusvelatusScaphiteshippocrepisPerisphinctestiziani

TrophitessubbullatusLeptodusamericanus

Cactocrinusmultibrachiatus

Dictyoclostusamericanus

Mucrospinifermucronatus

Cystiphyllumniagarense

Bathyurus extans

Paradoxides pinus

Neptunea tabulataVenericardiaplanicosta

InoceramuslabiatusNerinea trinodosa

Monotissubcircularis

Parafusilinabosei

Lophophyllidiumproliferum

Prolecanites gurleyi

Palmatolepusunicornis

HexamocarashertzeriTetragraptusfructicosus

Billingsellacorrugata

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This wrinkled "elephant skin" texture is atrace fossil of a non-stromatolite microbialmat.The image shows the location, in theBurgsvik beds of Sweden, where thetexture was first identified as evidence of amicrobial mat.[53]

Overview of the history of lifeMain article: Evolutionary history of lifeFurther information: Timeline of evolutionary history of life

The evolutionary history of life stretches back to over 3,000 million years ago, possibly as far as3,800 million years ago.[47] Earth formed about 4,570 million years ago and, after a collision that formedthe Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphereabout 4,440 million years ago.[48] However, there is evidence on the Moon of a Late Heavy Bombardmentfrom 4,000 to 3,800 million years ago. If, as seems likely, such a bombardment struck Earth at the sametime, the first atmosphere and oceans may have been stripped away.[49] The oldest clear evidence of life onEarth dates to 3,000 million years ago, although there have been reports, often disputed, of fossil bacteriafrom 3,400 million years ago and of geochemical evidence for the presence of life 3,800 million years ago.[9][50] Some scientists have proposed that life on Earth was "seeded" from elsewhere,[51] but most researchconcentrates on various explanations of how life could have arisen independently on Earth.[52]

For about 2,000 million years microbial mats, multi-layeredcolonies of different types of bacteria, were the dominant life onEarth.[54] The evolution of oxygenic photosynthesis enabledthem to play the major role in the oxygenation of theatmosphere[55] from about 2,400 million years ago. This changein the atmosphere increased their effectiveness as nurseries ofevolution.[56] While eukaryotes, cells with complex internalstructures, may have been present earlier, their evolutionspeeded up when they acquired the ability to transform oxygenfrom a poison to a powerful source of energy in theirmetabolism. This innovation may have come from primitiveeukaryotes capturing oxygen-powered bacteria asendosymbionts and transforming them into organelles calledmitochondria.[47][57] The earliest evidence of complexeukaryotes with organelles such as mitochondria, dates from1,850 million years ago.[21]

Multicellular life is composed only of eukaryotic cells, and the earliest evidence for it is the FrancevillianGroup Fossils from 2,100 million years ago,[58] although specialisation of cells for different functions firstappears between 1,430 million years ago (a possible fungus) and 1,200 million years ago (a probable redalga). Sexual reproduction may be a prerequisite for specialisation of cells, as an asexual multicellularorganism might be at risk of being taken over by rogue cells that retain the ability to reproduce.[59][60]

The earliest known animals are cnidarians from about 580 million years ago, but these are so modern-looking that the earliest animals must have appeared before then.[61] Early fossils of animals are rarebecause they did not develop mineralised hard parts that fossilise easily until about 548 million years ago.[62] The earliest modern-looking bilaterian animals appear in the Early Cambrian, along with several "weirdwonders" that bear little obvious resemblance to any modern animals. There is a long-running debate about

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Opabinia made thelargest singlecontribution to moderninterest in the Cambrianexplosion.

At about 13 centimetres(5.1 in) the EarlyCretaceous Yanoconodonwas longer than theaverage mammal of thetime.[73]

Birds are the last surviving dinosaurs.[74]

whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation; alternativeviews are that modern-looking animals began evolving earlier but fossils of their precursors have not yetbeen found, or that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups.[63]

Vertebrates remained an obscure group until the first fish with jaws appeared in the Late Ordovician.[64][65]

The spread of life from water to land required organisms to solve severalproblems, including protection against drying out and supporting themselvesagainst gravity.[66][67][68][69] The earliest evidence of land plants and landinvertebrates date back to about 476 million years ago and490 million years ago respectively.[68][70] The lineage that produced landvertebrates evolved later but very rapidly between 370 million years ago and360 million years ago;[71] recent discoveries have overturned earlier ideas aboutthe history and driving forces behind their evolution.[72] Land plants were sosuccessful that they caused an ecological crisis in the Late Devonian, until theevolution and spread of fungi that could digest dead wood.[23]

During the Permian period synapsids, including theancestors of mammals, may have dominated land environments,[75] but thePermian–Triassic extinction event 251 million years ago came very close towiping out complex life.[76] The extinctions were apparently fairly sudden, atleast among vertebrates.[77] During the slow recovery from this catastrophe apreviously obscure group, archosaurs, became the most abundant and diverseterrestrial vertebrates. One archosaur group, the dinosaurs, were the dominantland vertebrates for the rest of the Mesozoic,[78] and birds evolved from onegroup of dinosaurs.[74] During this time mammals' ancestors survived only assmall, mainly nocturnal insectivores, but this apparent set-back mayhave accelerated the development of mammalian traits such asendothermy and hair.[79] After the Cretaceous–Paleogene extinctionevent 65 million years ago killed off the non-avian dinosaurs – birdsare the only surviving dinosaurs – mammals increased rapidly in sizeand diversity, and some took to the air and the sea.[80][81][82]

Fossil evidence indicates that flowering plants appeared and rapidlydiversified in the Early Cretaceous, between 130 million years agoand 90 million years ago.[83] Their rapid rise to dominance ofterrestrial ecosystems is thought to have been propelled bycoevolution with pollinating insects.[84] Social insects appearedaround the same time and, although they account for only small parts of the insect "family tree", now formover 50% of the total mass of all insects.[85]

Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over6 million years ago.[86] Although early members of this lineage had chimp-sized brains, about 25% as big asmodern humans', there are signs of a steady increase in brain size after about 3 million years ago.[87] There

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A modern social insect collectspollen from a modern floweringplant.

Apparent extinction intensity, i.e. the fraction ofgenera going extinct at any given time, asreconstructed from the fossil record (graph not meantto include recent epoch of Holocene extinction event)

is a long-running debate about whether modern humans are descendantsof a single small population in Africa, which then migrated all over theworld less than 200,000 years ago and replaced previous homininespecies, or arose worldwide at the same time as a result ofinterbreeding.[88]

Mass extinctions

Main article: Mass extinction

Life on earth has suffered occasional mass extinctionsat least since 542 million years ago. Although theyare disasters at the time, mass extinctions havesometimes accelerated the evolution of life on earth.When dominance of particular ecological nichespasses from one group of organisms to another, it israrely because the new dominant group is "superior"to the old and usually because an extinction eventeliminates the old dominant group and makes way forthe new one.[89][90]

The fossil record appears to show that the rate ofextinction is slowing down, with both the gapsbetween mass extinctions becoming longer and theaverage and background rates of extinctiondecreasing. However, it is not certain whether theactual rate of extinction has altered, since both ofthese observations could be explained in severalways:[91]

The oceans may have become more hospitable to life over the last 500 million years and lessvulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greaterdepths; the development of life on land reduced the run-off of nutrients and hence the risk ofeutrophication and anoxic events; marine ecosystems became more diversified so that food chainswere less likely to be disrupted.[92][93]

Reasonably complete fossils are very rare, most extinct organisms are represented only by partialfossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenlyassigned parts of the same organism to different genera, which were often defined solely toaccommodate these finds – the story of Anomalocaris is an example of this.[94] The risk of this

Marine extinction intensity during thePhanerozoic

%

Millions of years ago

(H)

K–PgTr–J

P–Tr

Late DO–S

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Phanerozoic biodiversity as shown by the fossilrecord

This illustration of an Indianelephant jaw and a mammoth jaw(top) is from Cuvier's 1796 paperon living and fossil elephants.

mistake is higher for older fossils because these are often unlike parts of any living organism. Many"superfluous" genera are represented by fragments that are not found again, and these "superfluous"genera appear to become extinct very quickly.[91]

Biodiversity in the fossil record, which is

"the number of distinct genera alive at anygiven time; that is, those whose firstoccurrence predates and whose lastoccurrence postdates that time"[95]

shows a different trend: a fairly swift rise from542 to 400 million years ago, a slight decline from400 to 200 million years ago, in which the devastatingPermian–Triassic extinction event is an important factor,and a swift rise from 200 million years ago to the present.[95]

History of paleontologyMain article: History of paleontologyFurther information: Timeline of paleontology

Although paleontology became established around 1800, earlierthinkers had noticed aspects of the fossil record. The ancient Greekphilosopher Xenophanes (570–480 BC) concluded from fossil sea shellsthat some areas of land were once under water.[96] During the MiddleAges the Persian naturalist Ibn Sina, known as Avicenna in Europe,discussed fossils and proposed a theory of petrifying fluids on whichAlbert of Saxony elaborated in the 14th century.[97] The Chinesenaturalist Shen Kuo (1031–1095) proposed a theory of climate changebased on the presence of petrified bamboo in regions that in his timewere too dry for bamboo.[98]

In early modern Europe, the systematic study of fossils emerged as anintegral part of the changes in natural philosophy that occurred duringthe Age of Reason. At the end of the 18th century Georges Cuvier'swork established comparative anatomy as a scientific discipline and, byproving that some fossil animals resembled no living ones,demonstrated that animals could become extinct, leading to theemergence of paleontology.[99] The expanding knowledge of the fossilrecord also played an increasing role in the development of geology,particularly stratigraphy.[100]

All genera"Well-defined" generaTrend line"Big Five" mass extinctionsOther mass extinctions

Million years ago Thousands of genera

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Haikouichthys, from about518 million years ago in China,may be the earliest known fish.[106]

The first half of the 19th century saw geological and paleontological activity become increasingly wellorganised with the growth of geologic societies and museums[101][102] and an increasing number ofprofessional geologists and fossil specialists. Interest increased for reasons that were not purely scientific, asgeology and paleontology helped industrialists to find and exploit natural resources such as coal.[103]

This contributed to a rapid increase in knowledge about the history of life on Earth and to progress in thedefinition of the geologic time scale, largely based on fossil evidence. In 1822 Henri Marie Ducrotay deBlanville, editor of Journal de Phisique, coined the word "palaeontology" to refer to the study of ancientliving organisms through fossils.[104] As knowledge of life's history continued to improve, it becameincreasingly obvious that there had been some kind of successive order to the development of life. Thisencouraged early evolutionary theories on the transmutation of species.[105] After Charles Darwin publishedOrigin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths,including human evolution, and evolutionary theory.[105]

The last half of the 19th century saw a tremendous expansion inpaleontological activity, especially in North America.[107] The trendcontinued in the 20th century with additional regions of the Earth beingopened to systematic fossil collection. Fossils found in China near theend of the 20th century have been particularly important as they haveprovided new information about the earliest evolution of animals, earlyfish, dinosaurs and the evolution of birds.[108] The last few decades ofthe 20th century saw a renewed interest in mass extinctions and theirrole in the evolution of life on Earth.[109] There was also a renewedinterest in the Cambrian explosion that apparently saw the development of the body plans of most animalphyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extendedknowledge about the history of life back far before the Cambrian.[63]

Increasing awareness of Gregor Mendel's pioneering work in genetics led first to the development ofpopulation genetics and then in the mid-20th century to the modern evolutionary synthesis, which explainsevolution as the outcome of events such as mutations and horizontal gene transfer, which provide geneticvariation, with genetic drift and natural selection driving changes in this variation over time.[110] Within thenext few years the role and operation of DNA in genetic inheritance were discovered, leading to what isnow known as the "Central Dogma" of molecular biology.[111] In the 1960s molecular phylogenetics, theinvestigation of evolutionary "family trees" by techniques derived from biochemistry, began to make animpact, particularly when it was proposed that the human lineage had diverged from apes much morerecently than was generally thought at the time.[112] Although this early study compared proteins from apesand humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA.[113]

See alsoBiostratigraphyEuropean land mammal ageFossil collectingList of fossil sites (with link directory)

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List of notable fossilsList of paleontologistsList of transitional fossilsPaleogeneticsRadiometric datingTaxonomy of commonly fossilised invertebratesTreatise on Invertebrate Paleontology

Notes

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External linksSmithsonian's Paleobiology website (http://paleobiology.si.edu/)University of California Museum of Paleontology FAQ About Paleontology(http://www.ucmp.berkeley.edu/FAQ/faq.html)The Paleontological Society (http://www.paleosoc.org)

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ISBN 9780470022214.101. Greene, Marjorie; David Depew (2004). The Philosophy of Biology: An Episodic History. Cambridge University

Press. pp. 128–130. ISBN 0-521-64371-6.102. Bowler, Peter J.; Iwan Rhys Morus (2005). Making Modern Science. The University of Chicago Press. pp. 168–

169. ISBN 0-226-06861-7.103. Rudwick, Martin J.S. (1985). The Meaning of Fossils (2nd ed.). The University of Chicago Press. pp. 200–201.

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(History of Paleontology). Ayer Company Publishing. ISBN 978-0-405-12706-9.106. Shu, D. G.; Morris, S. C.; Han, J.; Zhang, Z. F.; Yasui, K.; Janvier, P.; Chen, L.; Zhang, X. L.; Liu, J. N.; Li, Y.;

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107. Everhart, Michael J. (2005). Oceans of Kansas: A Natural History of the Western Interior Sea. Indiana UniversityPress. p. 17. ISBN 0-253-34547-2.

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109. Bowler, Peter J. (2003). Evolution:The History of an Idea. University of California Press. pp. 351–352. ISBN 0-520-23693-9.

110. Bowler, Peter J. (2003). Evolution:The History of an Idea. University of California Press. pp. 325–339. ISBN 0-520-23693-9.

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The Palaeontological Association (http://www.palass.org)The Paleontology Portal (http://www.paleoportal.org)"Geology, Paleontology & Theories of the Earth"(http://lhldigital.lindahall.org/cdm/search/collection/earththeory), a collection of more than 100digitised landmark and early books on Earth sciences at the Linda Hall Library

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